Short answers, pulled from the story.
The three types of tundra are Arctic, Alpine, and Antarctic. Arctic tundra covers the far north of Russia and Canada, Alpine tundra occurs above the tree line on mountains worldwide, and Antarctic tundra is found on the Antarctic Peninsula and subantarctic islands such as South Georgia and the Kerguelen Islands.
Trees cannot grow in tundra because of frigid temperatures and short growing seasons. In Arctic tundra, the soil is frozen from 25 to 90 centimetres down, making it impossible for tree roots to penetrate; in alpine tundra, low air temperatures and altitude prevent tree establishment.
Permafrost is permanently frozen soil that lies beneath much of the Arctic tundra. It stores large amounts of carbon in the form of methane and carbon dioxide. When it thaws due to global warming, these greenhouse gases are released, creating a feedback cycle that further accelerates warming.
The Arctic tundra supports reindeer (caribou), musk ox, Arctic hare, Arctic fox, snowy owl, ptarmigan, northern red-backed voles, lemmings, and polar bears near the coast. The biome supports only 48 species of land mammals, though millions of birds migrate there each summer.
Only two flowering plant species grow in Antarctica: Antarctic hair grass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis). Both are found on the northern and western parts of the Antarctic Peninsula.
The word tundra first appeared in English in 1824, spelled "toundra," possibly borrowed through French from the Russian word. The Russian term may itself derive from the Sami word "tundar," meaning a fell or elevated wasteland, used from the 16th century.